Patent GB-1430094-A (GB)
Title: Porous glass articles
IPC: C03B20/00
Filed: 1973-03-01
Abstract: 1430094 Microporous glass PPG INDUSTRIES Inc 1 March 1973 [1 Dec 1972] 9973/73 Heading C1M [Also in Divisions B1-B2] A strong, thermally stable, microporous glass article having a pore volume of at least 0À35 c.c./gm., pore sizes of 50-200 , and a surface area of at least 100 m.<SP>2</SP>/gm., is composed of (a) at least 96% by weight SiO 2 , (b) less than 4% by weight B 2 O 3 , (c) less than 0À05% by weight alkali metal oxide, or alkaline earth metal oxide or PbO, CdO, ZnO or SnO, and (d) less than 0À4% by weight Al 2 O 3 ; and said microporous glass article has a crush strength of at least 20 lbs./sq. inch gauge and loses less than 30% of its original surface area and undergoes less than 25% volume shrinkage when subjected to a temperature of 980 C. for 24 hours. In a modification the highly microporous glass article has a pore volume of 0À5-0À7 c.c/gm., a pore size diameter of 200-1000 , a crush strength of 5-20 lbs./sq. inch gauge, and undergoes 10-20% volume shrinkage when subjected to 760 C. for 24 hours. The microporous glass article is preferably in particle form having a diameter of 0À05-5 mm. A borosilicate glass useful in the process for producing the glass articles comprises 30-50% by weight SiO 2 , 40-55% by weight B 2 O 3 , 5-15% by weight alkali metal oxide, such as K 2 O and Na 2 O, alkaline earth metal oxide such as BaO, CaO and MgO, PbO, CdO, SnO, and ZnO, and 0-4% by weight Al 2 O 3 . Such a glass is phase separable, the silica forming the insoluble phase. The borosilicate glass may first be particulated and beaded. Thereafter the glass beads are heated at 420-700 C. for 1-64 hours and this produces a glass having two distinct phases. Treatment at 420-500 C. for 1-8 hours will produce, after leaching, beads with average pore diameter of 50-200 , whilst beads treated at 580- 650 C. for 8-24 hours will produce beads with average pore diameter of 200-1000 . After cooling the beads are subjected to an extraction process. This involves a first water leach followed by a second acid leach. In the water leach the soluble borate-rich phase is dissolved out, suitably at 80-100 C. for 4-24 hours. Preferably an aqueous solution of metal borate is used. The volume of water to glass in this leaching should be 2-8 volumes of water to 1 volume of glass. The water solution containing the soluble phase is then separated from the beads. Subsequently the wet glass beads are transferred to an acid bath for a second leaching. Useful acids are mineral acids and oxalic acid. In general the acid leach is carried out at 80-100 C. for at least ¢ hour; e.g. 2-4 hours, the volume ratio acid to porous glass being 1-8 volumes acid to 1 volume glass. The porous glass particles may be used as catalyst supports and when the article is pre-shrunk by 5-20% of its original volume it undergoes less than 10% volume shrinkage when subjected to a temperature of 980 C. for 24 hours. Catalysts may be impregnated into the porous particles by soaking the particles in solution or by vapour depositing the catalyst in the pores. Suitable catalysts incorporated therein are Pt, Pd, TiO 2 , V 2 O 5 , Cr 2 O 3 , FeO, CoO, NiO 2 , CuO, Al 2 O 3 , ZrO 2  and SnO 2 . A deposited metal oxide may be subsequently reduced to the metal by passing a stream of hydrogen gas over the support. Example IV refers to treating beads with SnCl 4 .5H 2 O, Al(NO 3 ) 3 .9H 2 O, CrCl 3 .6H 2 O and ZrOCl 2 .8H 2 O solutions and subsequent calcination to form the oxides.